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Bulletin  273 


January,  1926 


(Euuurrttrut  Agricultural  iExurrtmrut  ^tattuu 
£faw  ijatiftt,  Qlomiprttrut 


Crossed  Corn 


s 

Bulletin  273  January,  1926        tToJO 

Qlontiprttntt  Agrtrultural  {Expmmrttt  Station 

N* ro  lHaupn,  (EDuttrrttrut 


CROSSED  CORN 

D.  F.  JONES 
P.  C.  MANGELSDORF 


The  Bulletins  of  this  Station  are  mailed  free  to  citizens  of  Connecticut 
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CONNECTICUT   AGRICULTURAL   EXPERIMENT  STATION 

OFFICERS  AND  STAFF 
January,  1926 


BOARD  OF  CONTROL. 
His  Excellency,  John  H.  Trumbull,  cx-officio,  President. 

Charles  R.  Treat,  Vice-President Orange 

George  A.  Hopson,  Secretary   Mount  Carmel 

Wm.  L.  Slate,  Jr.,  Director  and  Treasurer  New  Haven 

Joseph  W.  Alsop Avon 

Elijah  Rogers  Southington 

Edward   C.   Schneider    Middletown 

Francis  F.  Lincoln Cheshire 


Administration. 


Chemistry. 
Analytical  Laboratory. 


Biochemical 
Laboratory. 

Botany. 


Entomology. 


Forestry. 

Plant  Breeding. 
Soil  Research. 


Tobacco  Sub-station 
at  Windsor. 


STAFF. 
E.  H.  Jenkins,  Director  Emeritus. 

Wm.  L.  Slate,  Jr.,  B.Sc,  Director  and  Treasurer. 
Miss   L.  M.  Brautlecht,  Bookkeeper  and  Librarian. 
Miss  J.   V.  Berger,  Stenographer  and  Bookkeeper. 
Miss  Mary   E.   Bradley,   Secretary. 
G.  E.  Graham,  In  charge  of  Buildings  and  Grounds. 

E.  M.  Bailey,  Ph.D.,  Chemist  in  Charge. 

K.    h.   Andrew,  M.A. 

C.  E.  Shepard 

Owen  L.  Nolan  V    Assistant  Chemists. 

Harry  J.  Fisher,  A.B. 

W.   T.   Mathis  J 

Frank  C.  Sheldon,  Laboratory  Assistant. 

V.  L.  Churchill,  Sampling  Agent. 

Miss  Mabel  Bacon,  Stenographer. 

T.  B.  Osborne,  Ph.D.,  Chemist  in  Charge. 


G.  P.  Clinton,  Sc.D.,  Botanist  in  Charge. 

E.  M.  Stoddard,  B.S.,  Pomologist. 

Miss  Florence  A.  McCormick,  Ph.D.,  Pathologist. 

Willis  R.  Hunt,  Ph.D.,  Assistant  in  Botany. 

A.  D.  McDonnell,  General  Assistant. 
Mrs.  W.  W.  Kelsey,  Secretary. 

W.  E.  Britton,  Ph.D.,  Entomologist  in  Charge;    State  Ento- 
mologist. 

B.  H.  Walden,  B.Agr.       ) 

M.   P.   Zappe,   B.S.  V     Assistant  Entomologists. 

Philip  Carman,  Ptt.D.       ' 

Roger  B.  Friend,  B.S.,  Graduate  Assistant. 

John  T.  Ashworth,  Deputy  in  Charge  of  Gipsy  Moth  Work. 

R.  C.  Botsford,  Deputy  in  Charge  of  Mosquito  Elimination. 

Miss  Gladys  M.  Finley,  Stenographer. 

Walter  O.  Filley,  Forester  in  Charge. 
H.   W.   Hicock,  M.F.,  Assistant  Forester. 
Miss  Pauline  A.  Merchant,  Stenographer. 

Donald  F.  Jones,  S.D.,  Geneticist  in  Charge. 
P.  C.  Mangelsdorf,  S.D.,  Assistant  Geneticist. 

M.  F.  Morgan,  M.S.,  Investigator. 

George  D.   Scarseth,  B.S.,    Graduate  Assistant. 

Paul  J.  Anderson,  Ph.D.,  Pathologist  in  Charge. 
N.  T.  Nelson,  Ph.D.,  Assistant  Physiologist. 


THE    TUTTLE,     MOREHOUSE    &    TAYLOR     COMPANY 


CROSSED  CORN 

D.  F.  Jones  and  P.  C.  Mangelsdorf. 


Vigorous,  sturdy  plants,  a  good  sound  ear  on  every  stalk,  no 
weak  and  spindling  plants,  few  nubbins  or  moldy  ears.  These 
are  some  of  the  outstanding  characteristics  of  crossed  corn.  It  is 
all  these  desirable  features  combined  that  enable  this  new  kind  of 
corn  to  outyield  the  old  standard  varieties,  year  after  year,  and 
under  all  sorts  of  conditions. 

Crossing  two  distinct  types  of  animals  or  of  plants  almost 
always  causes  an  increase  in  vigor.  This  has  long  been  known 
and  used  in  the  production  of  mules,  sterile  hybrids  of  the  horse 
and  the  ass.  Swine  breeders  often  utilize  the  beneficial  effects 
of  hybrid  vigor  by  crossing  different  breeds  of  pigs,  feeding  for 
market  the  hybrid  offspring  but  not  breeding  from  them. 

The  same  principle  can  be  used  in  increasing  the  yield  of  corn 
and  the  Connecticut  Agricultural  Experiment  Station  has  been 
working  for  many  years  to  find  the  best  methods  of  utilizing  hybrid 
vigor  and  to  produce  strains  of  corn  for  crossing  that  give  high 
yields  adapted  to  the  cultural  and  market  requirements  of  this 
region. 

Several  promising  types  of  crossed  corn  have  now  been  pro- 
duced, of  which  stock  seed  is  available  for  seed  growing.  Other 
types  are  now  being  developed  to  meet  different  requirements 
and  these  will  soon  be  available  for  distribution. 

The  uniform  production  from  every  plant,  though  the  most 
important  feature,  is  only  one  of  the  desirable  characteristics  of 
crossed  corn.  The  ears  are  more  even  in  size  and  shape,  there 
are  fewer  nubbins,  poorly  developed  ears  and  moldy  corn.  Many 
combinations  show  appreciably  less  smut  and  root  rot  infection. 
The  stalks  themselves  are  sturdy  and  strong  and  stand  up  when 
other  plants  are  laid  low  by  wind  and  rain.  In  time  of  tasseling 
and  silking  the  crossed  plants  are  far  more  even  than  ordinary 
varieties  and  in  ripening  there  is  the  same  remarkable  uniformity. 

In  crossed  sweet  corn  this  uniformity  in  time  of  ripening  is  a 
very  valuable  feature  for  the  market  gardener  or  canner.  It 
enables  the  grower  to  harvest  his  crop  at  one  time  and  have 
practically  all  of  the  ears  ready  to  be  picked.  This  results  in  a 
better  quality  of  canned  or  table  corn,  because  fewer  immature 
and  over-ripe  ears  are  included. 

The  uniform  size  of  the  ears  is  also  particularly  desirable  in 
the  case  of  sweet  corn.  It  makes  for  a  more  attractive  product 
and  is  a  feature  that  appeals  especially  to  the  restaurant  trade. 


154  CONNECTICUT    EXPERIMENT    STATION  BULLETIN    273 

SEED  SELECTION. 

The  uniformity  of  crossed  corn,  its  evenness  in  ripening,  its 
increased  productiveness,  the  greater  freedom  from  disease,  cannot 
be  obtained  by  any  of  the  usual  methods  of  seed  selection  in 
naturally-pollinated  fields  of  corn. 


Fig.  1. — Vigorous,  sturdy  plants  with  a  good  ear 
characteristic  of  crossed  corn. 


>n  every  stalk  are 


One  may  go  through  a  field  or  crib  of  corn,  picking  out  the 
largest  and  finest  ears,  discarding  all  poorly  filled  and  moldy  ears 
and  keeping  only  the  one  best  ear  out  of  every  thousand,  and  yet 
these  choice  specimens  do  not  reproduce  their  excellence ;  they  do 
not  "breed  true."  No  matter  how  fine  in  appearance  are  the 
ears  which  are  planted,  they  always  give  many  weak  plants  and 
non-producers. 

The  failure  of  the  finest  ears  to  reproduce  themselves  has 
several  causes.     It  is  due,  in  part,  to  the  fact  that  many  of  the  best 


CROSSED    CORN 


'55 


ears  are  good,  not  because  of  their  heredity  but  because  of  the 
especially  favorable  situation  in  which  they  grew.     It  is  solely 


Fig.  2. — In  size  and  shape  of  ear  and  in  time  of  ripening  there  is  a 
remarkable  uniformity. 

their  environment  that  has  made  them  better  than  the  average 
and  the  effects  of  environment,  we  now  know,  can  not  be  passed 
on  to  later  srenerations. 


»56 


CONNECTICUT    EXPERIMENT    STATION 


BULLETIN    273 


The  main  reason,  however,  that  the  selected  ears  do  not  breed 
true  lies  in  the  fact  that  the  pollen  which  produced  their  seeds 
came  from  all  sorts  of  plants.  Every  silk  must  receive  pollen 
in  order  for  a  seed  to  develop.  The  pollen  is  shed  by  the  tassels 
and  good,  poor  and  indifferent  plants  alike  send  their  pollen  into 
the  air  where  it  is  mixed  by  the  wind  and  carried  to  all  parts  of 
the  corn  field.  The  choicest  ear  in  the  entire  field  has  received 
part  of  its  pollen  from  some  of  the  poorest  neighbors. 


Fig.  3. — The  plants  grown  from  the  small  ears  were  just  as  large  and 
the  yield  of  shelled  grain  was  the  same  as  from  the  large  seed  ears. 


This  constant  inter-crossing  and  hereditary  mixing  going  on  in 
every  corn  field  has  brought  about  a  condition  whereby  every  plant 
is  a  hybrid  of  greater  or  less  degree  of  complexity  and  the  off- 
spring of  hybrids  are  usually  diverse  and  seldom  like  their  parents. 
Moreover,  corn  has  been  naturally  crossed  in  this  way  for  count- 
less years  and  is  dependent  upon  hybrid  vigor  to  produce  its 
largest  yield. 

In  spite  of  the  natural  crossing  which  is  constantly  going  on, 
it  is  possible  by  ordinary  field  selection,  patiently  practiced,  year 
after  year,  to  bring  about  an  improvement  in  certain  respects.  By 
saving  for  seed  only  the  ears  from  the  earliest  ripening  plants 
one  may  in  time  develop  a  variety  that  will  mature  somewhat 


CROSSED   CORN  157 

earlier.  By  choosing  plants  with  many  ears,  the  average  number 
of  ears  per  stalk  can  be  gradually  increased.  Noticeable  changes 
can  be  made  in  the  number  of  rows  of  grain  on  the  ear,  the  size 
and  shape  of  the  ear  or  the  type  of  kernel. 

Selection  of  this  kind  is  usually  made  with  some  definite  aim 
of  adapting  the  variety  more  perfectly  to  the  purpose  for  which 
it  is  grown.  Such  alterations  are  seldom  accompanied  by  any 
increase  of  yield  and  often,  particularly  where  extreme  earliness 
is  sought,  productiveness  is  lowered. 

Tests  carried  out  at  many  places  have  shown  that  the  prize 
winning  ears  at  the  corn  shows  often  yield  no  more  than  unselected 
ears  that  are  much  less  desirable  in  appearance.  This  fact  is 
brought  out  in  the  accompanying  illustration.  Plants  grown  from 
the  nubbins  at  the  right  were  just  as  strong  as  those  produced 
by  the  good  ears  shown  on  the  left.  The  ears  were  fully  as 
large  and  the  yield  of  shelled  corn  was  exactly  the  same. 

In  this  case  the  difference  in  appearance  of  the  two  lots  of 
seed  ears  was  not  due  to  heredity  but  merely  to  the  conditions  in 
the  field  in  which  they  grew,  the  one  in  a  good  situation,  the  other 
in  a  poor  one. 

THE  EAR-TO-ROW  METHOD  OF  SELECTION. 

When  the  seed  from  a  number  of  ears  of  corn  are  planted  sep- 
arately, each  in  a  row  by  itself,  some  lots  grow  better  and  yield 
considerably  more  than  others.  It  was  formerly  thought  that  by 
selecting  seed  from  the  high  producing  rows  or  planting  the  remain- 
ing seed  from  the  best  yielding  mother  ears,  and  continuing  this 
process  from  year  to  year,  an  increase  in  yield  could  be  obtained. 
A  marked  increase  in  yield  is  sometimes  obtained  the  first  year  or 
two  but  extensive  tests  have  shown  that  the  differences  are  not 
permanent  and  that  in  later  generations  the  yield  from  the  orig- 
inally high  producers  is  no  more  than  that  obtained  from  the 
unselected  seed. 

The  failure  of  the  high  producing  ears  to  maintain  their 
increased  yields  is  probably  due  to  their  hybrid  composition.  They 
split  up  and  lose  vigor  in  later  generations.  Selection  towards  a 
single  type  also  brings  about  a  certain  amount  of  inbreeding  which 
always  weakens  the  plants. 

HYBRID  VIGOR. 

Crossing  somewhat  different  but  related  forms  of  plants  or 
animals  results  in  greater  growth,  the  offspring  often  being  better 
than  either  parent.  Blue-gray  cattle  have  long  been  used  for 
beef  in  Scotland.  They  are  the  result  of  crossing  a  white  Short- 
horn bull  and  black  Gallowav  or  Angus  cows.     The  large  growth. 


'58 


CONNECTICUT    EXPERIMENT    STATION- 


BULLETIN    273 


early  maturity  and  fine  beef  quality  has  given  this  breed  cross 
an  enviable  reputation  whereever  beef  cattle  are  raised. 

The  Carolina  poplar  is  a  thrifty,  fast-growing-  tree  that  succeeds 
well  in  nearly  all  parts  of  the  country.     It  is  considered  to  be  a 


Fig.  4. — Two  dwarf  types  of  corn  give  an  astonishing  result  when 
crossed. 


natural  hybrid  between  the  Cottonwood  of  our  western  plains  and 
the  European  Black  poplar.  A  valuable  feature  of  this  tree  is  the 
ease  with  which  it  can  be  grown  from  cuttings.  Its  vigorous 
nature  is  thus  easily  maintained  while  at  the  same  time  the  trees 
are  multiplied  in  numbers. 

Hybrid  vigor  is  usually  responsible   for  part  of  the  value  of 
most  vegefatively  propagated  plants.     As  long  as  they  are  not 


CROSSED    CORN 


*59 


reproduced  from  seeds  the  stimulus  to  increased  growth  is  main- 
tained undiminished.  In  naturally  cross-pollinated  plants  it  is 
necessary  to  keep  up  a  constant  intercrossing  in  order  to  maintain 
full  vigor. 

The  corn  plant  is  so  constructed  with  its  tassel,  the  pollen- 
bearing  structure,  at  the  top  of  the  stalk,  that  it  can  be  easily 
detasseled  before  pollen  is  shed,  thereby  entirely  preventing  self- 
fertilization.  Fifty  years  ago  a  method  was  outlined  whereby 
two  varieties  of  corn  could  be  crossed  by  planting  them  in  alternat- 


Fig.  5. — The  corn  plant  is  so  constructed  that  it  can  easily  be  crossed 
by  planting  in  alternating  rows  and  detasseling  all  of  the  plants  of 
one  kind  before  pollen  is  shed. 


ing  rows  and  pulling  out  all  the  tassels  of  one  variety  before  pollen 
is  shed.  All  of  the  seeds  borne  on  such  emasculated  plants  must 
result  from  cross-pollination  of  one  variety  with  another. 

Numerous  tests  have  shown  that  an  increased  yield  often  results 
when  certain  varieties  of  different  type,  such  as  flint  and  dent,  are 
crossed.  Some  varieties  of  corn  from  China  when  crossed  with 
native  varieties  have  given  considerably  larger  yields  than  either 
parent.  Crossing  an  early  variety  with  a  late  variety  sometimes 
gives  a  cross-bred  progeny  that  yields  as  much  as  the  later  parent 
and  is  appreciably  earlier.  Varieties  of  similar  type  when  com- 
bined have  not  given  much  better  results  than  either  parent. 

The  increased  yields  which  are  obtained  come  only  the  first 
year  after  crossing.  To  get  the  benefit  of  hybrid  vigor  in  plants 
reproduced  by  seeds  it  is  necessary  to  make  the  cross  each  year 
and  plant  only  the  crossed  seed.     Any  improvement  in  yield  or 


i6o 


CONNECTICUT    EXPERIMENT    STATION 


BULLETIN    273 


in  other  respects  must  be  great  enough  to  repay  the  extra  cost  of 
producing  seed  in  this  way.  Variety  crosses,  while  better  than 
their  parental  stocks  in  some  cases,  have  not,  apparently,  offered 
sufficient  improvement  to  induce  corn  growers  to  make  a  practical 
application  of  this  method. 


Fig.  6. — The  result  of  seven  generations  of  inbreeding. 


INBREEDING  BEFORE  CROSSING. 

A  larger  increase  in  yield  together  with  a  much  greater  uni- 
formity and  fixity  of  type  is  obtained  by  first  inbreeding  corn 
by  artificial  hand  pollination  for  several  years  and  then  crossing 
two  different  inbred  strains.  This  is  shown  in  the  accompanying 
illustration.  A  variety  of  Learning  which  yielded  96  bushels  per 
acre  was  inbred,  that  is,  the  silks  were  artificially  pollinated  with 
pollen  from  the  same  plants.  After  five  years  of  inbreeding  two 
strains,  one  of  which  had  been  reduced  in  yield  to  32  bushels  per 
acre,  the  other  to  20  bushels,  were  crossed.  The  first  genera- 
tion cross  of  these  two  low  yielding,  inbred  strains  produced  115 
bushels,  an  increase  of  twenty  per  cent  over  the  original  variety, 
under  the  same  conditions.  Not  only  did  this  hybrid  exceed  the 
original  variety  by  twenty  per  cent  in  yield  but  the  corn  was  of 
better  quality.  The  ears  were  all  closely  alike  in  size  and  shape 
and  all  matured  at  practically  the  same  time.  Every  stalk  bore 
a  good  ear  and  there  were  fewer  moldy  ears,  nubbins  and  less 
soft  corn. 


CROSSED    CORN  l6l 

Here  is  a  marked  improvement  secured  by  crossing.  Unfor- 
tunately this  particular  cross  and  many  other  combinations  made 
in  the  early  years  of  these  experiments  were  not  well  adapted  to 
Connecticut  conditions.  The  plants  ripened  too  late  to  make  a 
satisfactory  corn  for  husking  and  the  stalks  were  not  large  enough 
to  make  a  good  silage  variety.  Also  the  low  yields  and  poor 
quality  of  the  inbred  strains  made  it  practically  impossible  to 
produce  crossed  seed  in  quantity  and  at  a  price  that  would  justify 
its  use. 

At  the  present  time  every  effort  is  being  made  at  this  station  and 
throughout  the  corn-growing  states  to  produce  inbred  strains  that 


Fig.  7. — The  two  inbred  strains  were  derived  from  the  variety  on  the  left 
and  gave  the  result  on  the  right  when  crossed — 115  bushels  per  acre. 

will  give  hybrid  combinations  well  adapted  to  the  local  needs  and 
which  will  be  themselves  sufficiently  vigorous  and  productive  to 
make  the  growing  of  crossed  seed  commercially  profitable.  Other 
methods  of  utilizing  inbred  strains  of  corn  are  being  developed. 

Crossed  corn  seed  has  now  been  grown  in  Connecticut  five 
years  and  tested  long  enough  to  show  its  possibilities.  Two 
crosses  of  inbred  strains  outyielded  all  varieties  in  the  Iowa  corn 
yield  contest  in  1924  in  the  south  central  section.  One  of  the 
inbred  strains  used  in  one  of  these  crosses  was  developed  at  this 
station. 

A  combination  of  four  inbred  strains  known  as  Double  Crossed 
Burr-Learning  has  been  tested  for  five  years  in  comparison  with 
the  highest  yielding  varieties  grown  in  this  part  of  the  country 
with  the  following  results : 

r-Bushels  of  shelled  corn  per  acre—-, 
Highest  Yielding  Varieties 

D.  C.  Burr-Leaming  . 
Beardsley's  Learning  . 

Luce's   Favorite    

Webber's  Dent    

Northern  White  Dent 
Century  Dent    


1018 

i<pto 

1920 

1921 

1922 

Average 

116 

88 

55 

95 

63 

83 

Q6 

54 

5i 

85 

48 

67 

79 

38 

81 

50 

62 

81 

62 

57 

73 

49 

64 

84 

75 

32 

87 

69 

68 

5i 

55 

77 

67 

64 

162  CONNECTICUT    EXPERIMENT    STATION  BULLETIN    273 


Fig.  8. — The  uniform  production  of  a  good  ear  from  every  stalk 
gives  high  yields. 


Fig.  9. — Double  Crossed  Burr-Learning  grown  at  Durham,  Connecticut. 


Double  Crossed  Burr-Learning  has  been  grown  in  many  other 
parts  of  the  state  and  in  various  places  in  the  corn-growing  districts 


CROSSED    CORN 


16 


south  and  west.  In  most  cases  it  has  out-yielded  all  other  varie- 
ties, the  stalks  have  stood  erect  in  the  fields  until  harvest  and  the 
leaves  have  remained  green  until  the  ears  are  well  glazed. 

A  cross  of  two  inbred  strains  of  sweet  corn  grown  for  canning 
has  yielded  six  tons  of  ears  per  acre  in  comparison  with  three  and 
one-half  tons  from  Evergreen  corn. 


Fig.  io. — Weak  golden   colored  plants   when   crossed   with   dwarfs 
give  all  tall  and  vigorous  progeny. 


WHAT  INBREEDING  DOES. 

Many  abnormal  or  freak  types  of  corn  are  known,  such  as  dwarf 
plants,  golden  plants,  which  lack  the  normal  green  coloring"  matter 
necessary  to  manufacture  food,  liguleless  plants,  with  upright 
instead  of  spreading  leaves,  and  other  characters  which  seriously 
weaken  the  plants  and  reduce  their  ability  to  produce  grain.  These 
abnormalities  are  inherited  and  pure  breeding  strains  can  be 
maintained  from  vear  to  vear. 


164 


CONNECTICUT   EXPERIMENT    STATION 


BULLETIN    273 


When  one  of  these  unusual  types  is  crossed  with  a  normal  plant 
only  normal  plants  are  produced  in  the  first  generation  but  the 
abnormality  reappears  in  the  second  generation  and  may  be  recov- 
ered and  made  to  breed  true  again,  showing  that  these  weakening 
characters  are  hereditary. 

When,  for  example,  a  golden-leaved,  liguleless  plant  is  crossed 
with  a  dwarf  form  there  result  in  the  first  following  generation 
only  vigorous,  tall  growing,  dark  green  plants  with  spreading 


Fig.  11. — The  second  generation  from  the  cross  of  golden,  liguleless  and 
dwarf.    Eight  different  combinations  of  these  characters  are  obtained. 


leaves,  all  normal  in  every  respect,  uniformly  vigorous  and  produc- 
tive as  shown  in  Figure  10. 

Self-fertilizing  these  plants  or  allowing  them  to  inter-pollinate 
gives  an  astonishing  medley  of  plants  in  the  next  generation. 
There  will  be  dwarf  plants,  golden  plants  and  liguleless-leaved 
plants  and  some  with  two  and  even  three  of  these  abnormal  char- 
acters combined  in  one  individual.  There  will  be  some  plants  that 
are  normal  in  all  characters  but  very  few  will  be  as  vigorous  or 
productive  as  the  first  crossed  plants. 

The  difference  between  the  first  and  the  second  generation  in 
respect  to  uniformity,  size  and  productiveness  is  a  very  striking 
illustration  of  the  bad  effects  of  inbreeding.  This  is  an  extreme 
example  but  the  same  principle  holds  with  naturally  cross-fertilized 


CROSSED    CORN 


165 


plants  and  with  bisexual  animals.     In  most  cultivated  plants  such 
clear-cut  abnormalities  are  not  involved. 

When  any  ordinary  variety  of  corn  is  self-pollinated  there  is  a 
noticeable  reduction  in  size  and  yield  and  this  usually  continues 
for  five  or  six  generations.     From  this  point  on  there  is  seldom 


Fig.  12.— The  descendants  of  a  single  plant  after  four  generations 
of  self-fertilization. 


Fig.  13. — The  plants  within  an  inbred  line  are  all  closely  alike  but 
differ  from  every  other  line. 


any  further  reduction.  The  plants  in  these  generations,  in  any 
one  strain,  come  to  be  all  closely  alike  and  remain  fixed  in  their 
type  from  then  on  as  long  as  they  are  not  outcrossed  to  plants 
of  different  ancestry. 

Every  inbred  strain  descending  from  individual  plants  at  the 
start  is  different  to  a  greater  or  less  extent  from  every  other 
strain  even  though  they  all  come  from  the  same  variety.  Some 
are  tall,  others  short.     In  color  of  leaves,  silks  and  glumes,  great 


1 66 


CONNECTICUT   EXPERIMENT    STATION  BULLETIN    2/3 


diversity  is  found  and  in  the  size  and  shape  of  the  ears,  time  of 
ripening,  ability  to  stand  erect  and  in  number  and  size  of  tillers 
there  is  marked  dissimilarity.  Productiveness  ranges  all  the  way 
from  little  or  nothing  up  to  a  fair  yield  for  inbred  plants  but  no 


Fig.  14. — Crossing  inbred   strains  immediately  restores   vigor   and 
productiveness. 


CROSSED    CORN 


167 


inbred  strains  have  been  obtained  which  are  as  productive  as  the 
original  variety  and  usually  the  yields  are  reduced  to  less  than 
half  and  the  size  of  the  seed  and  quality  of  the  grain  are  propor- 
tionately lowered. 

Since  all  of  the  plants  within  an  inbred  line  come  to  be  closely 
alike  it  makes  no  difference  from  that  point  on  whether  the  plants 
are  self -fertilized  or  are  allowed  to  inter-cross  among  themselves. 
Their  size  and  productiveness  remain  the  same  as  long  as  pollen 
from  all  other  kinds  of  corn  is  kept  away  from  them. 

When  an  inbred  strain  is  crossed  with  another  strain  from  the 


Fig.  15. — When  rightly  grown,  crossed  corn  has  no  barren  stalks  or  poor 
producers. 


same  or  different  variety  there  is  a  very  great  increase  in  size  and 
yield  in  the  next  generation  as  we  have  already  seen.  In  size  the 
crossed  plants  are  as  large  or  larger  than  the  original  variety  and 
in  yield  of  grain  they  are  often  superior. 

This  is  due  apparently  to  the  fact  that  the  good  qualities  of 
both  parents  are  expressed  in  the  offspring  while  the  weak  qualities 
are  covered  over  for  the  time  being.  Thus  in  the  cross  of  golden, 
liguleless  with  dwarf  the  offspring  are  normal  in  every  respect. 
The  yellow  foliage  color,  the  upright  posture  of  the  leaves  and  the 
dwarfness  of  the  stalk  are  all  suppressed  in  this  generation.  What 
one  parent  lacks  is  supplied  by  the  other,  and  conversely.  Hybrid 
vigor  seems  to  be  a  wise  provision  on  the  part  of  nature  to  enable 
the  offspring  to  make  the  best  of  bad  ancestry. 

While  most  of  the  inbred  strains  do  not  have  freak  characters 
they  are  all  lacking  something  which  makes  for  full  size  and  pro- 
ductiveness.    Crossing  any  two  strains  usually  brings  back  suffi- 


1 68  CONNECTICUT   EXPERIMENT    STATION  BULLETIN   273 

cient  vigor  to  make  the  plants  as  productive  as  the  original  variety 
while  certain  combinations  are  very  much  superior. 

The  greater  production  of  crosses  of  inbred  strains  is  not  due 
so  much  to  the  large  size  of  the  ears  as  to  the  fact  that  every 
plant,  if  given  an  equal  opportunity  to  grow,  produces  a  good 
ear.  Some  of  the  ears  of  the  original  variety  may  be  larger  and 
finer  than  any  produced  by  the  hybrid  but  for  every  plant  of  this 
kind  there  are  many  stalks  that  have  only  nubbins  and  even  some 
that  are  entirely  barren. 

The  uniform  production  of  an  average  good  ear  from  every 
plant  is  largely  responsible  for  the  high  yield  of  crossed  corn. 
The  even  size  and  maturity  also  have  distinct  value  in  sweet  corn 
for  market  gardening  and  canning. 


HYBRID  VIGOR  NOT  PERMANENT. 

These  desirable  results  are  obtained  only  the  first  year  after 
crossing.  The  second  generation  grown  from  the  fine  looking 
hybrid  ears  fall  off  in  yield  about  20  per  cent  as  a  general  rule. 
While  the  amount  of  reduction  may  differ  greatly  this  result 
always  follows  when  hybrid  corn,  no  matter  how  vigorous  it  may 
be,  is  used  again  for  seed.  This  holds  true  whether  the  crossed 
plants  are  self-fertilized  artificially  or  are  allowed  to  inter- 
pollinate  naturally. 

A  cross  of  two  inbred  strains  grown  six  years  averaged  101 
bushels  per  acre.  The  second  generation  of  this  cross  from  self- 
pollinated  first  generation  plants  grown  the  same  years  and  com- 
pared under  equal  conditions  gave  an  average  of  69  bushels,  a 
decrease  of  more  than  30  per  cent. 

The  Nebraska  Station  compared  the  first  and  second  generations 
of  eight  hybrid  combinations  during  two  seasons  and  obtained 
an  average  of  52.2  and  27.8  bushels  per  acre  respectively  for  the 
two  successive  generations.  The  original  variety  from  which  the 
inbred  strains  were  derived  gave  41.7  bushels  in  the  same  period. 
In  this  case  the  reduction  in  yield  from  the  first  to  the  second 
generation  is  nearly  50  per  cent.  The  second  generation  was 
grown  from  seed  produced  by  inter-pollinating  the  first  generation 
plants. 

Not  only  is  there  this  decided  decrease  in  yield  but  uniformity 
is  also  lost.  In  size  and  shape  of  ear,  height  of  plant  and  in  time 
of  ripening  the  second  generation  is  even  more  variable  than 
ordinary  varieties. 

If  the  second  generation  is  again  inbred  the  whole  story  of  the 
production  of  inbred  strains  is  repeated.  There  is  a  continued 
decrease  in  size  and  yield,  as  in  the  first  period  of  inbreeding,  and 
the  reduction  continues  for  about  the  same  number  of  generations. 


CROSSED   CORN  169 

five  to  seven  on  the  average,  until  uniformity  and  constancy  are 
again  reached.  The  inbred  plants  are  generally  no  more  vigorous 
than  those  of  the  previous  inbreeding  although  they  differ  from 
their  parental  strains  and  from  each  other  in  minor  characteristics. 
In  other  words  hybrid  vigor  is  a  transitory  effect  and  ordinarily 
can  not  be  fixed  and  made  permanent  except  in  plants  propagated 
vegetatively.  Varieties  of  fruits,  vegetables  and  flowers  that  are 
reproduced  by  tubers,  roots,  grafts  or  other  asexual  methods  of 
propagation  owe  their  value  to  a  superior  combination  of  heredi- 
tary factors  which  produce  the  qualities  desired  and  which  also 
give  plants  a  large  amount  of  hybrid  vigor.  This  is  shown  by 
their  seedlings  which  are  almost  invariably  weaker  and  poorer  in 
many  respects. 


Fig.  16. — The  first  generation  cross  of  two  inbred  strains  will  not 
continue  to  give  as  satisfactory  results  the  next  year.  If  inbred  it 
will  decline  in  vigor  as  in  the  first  period  of  inbreeding. 


Unfortunately  from  the  standpoint  of  utilizing  hybrid  vigor, 
corn  can  not  be  reproduced  in  any  way  except  by  seeds.  It  can, 
however,  be  easily  crossed.  For  that  reason  it  is  feasible  to  pro- 
duce crossed  seed  for  planting  each  year  and  grow  only  the  first 
generation  hybrid  plants  for  production  of  sweet  corn  ears,  grain 
or  silage. 

The  additional  cost  of  crossed  seed  is  more  easily  justified  for 
corn  than  for  other  crops  because  the  cost  of  seed  is  a  smaller 
item  in  the  outlay  for  producing  a  crop  of  corn  than  for  any  other 
plant  commonly  grown. 


SELECTION  IN  SELF-FERTILIZED  LINES. 

The  character,  productiveness  and  general  value  of  any  com- 
bination of  inbred  strains, can  not  be  accurately  determined  from 
the  inbred  strains  themselves.  Many  strains  which  are  weak  and 
undesirable  in  their  inbred  condition  give  astonishing  results  when 


17°  CONNECTICUT    EXPERIMENT    STATION  BULLETIN    273 

crossed.  It  is  necessary  therefore  to  test  out  many  combinations 
to  secure  the  ones  that  have  outstanding  value. 

Not  all  crosses  of  inbred  strains  are  superior  to  the  original 
variety  and  like  every  other  good  product  crossed  corn  requires 
extensive  selection  and  much  thorough  testing  in  order  to  obtain 
something  of  real  merit. 

To  have  a  reasonable  chance  of  securing  a  good  combination, 
many  inbred  strains  must  be  obtained  and  then  tested  in  many 
combinations.  This  work  for  the  present  can  best  be  done  by  the 
State  Experiment  Stations  and  the  Federal  Department  of  Agri- 
culture until  the  method  is  more  generally  used.  The  prospect 
of  obtaining  a  particularly  fine  combination  and  being  able  to 
control  the  stock  strains  from  which  this  cross  is  obtained  holds 
out  an  inducement  to  originate  valuable  inbred  strains.  Never 
before  in  agricultural  history  has  a  seedsman  been  able  to  control 
a  valuable  plant  improvement. 

He  who  invents  a  new  machine  or  a  new  process  of  manufac- 
turing can  patent  his  product  and  reap  a  reward  for  his  industry 
and  inventiveness.  The  originator  of  a  new  and  improved  plant 
or  animal  ordinarily  loses  control  of  his  product  as  soon  as  he  sells 
his  first  seeds  or  breeding  stock. 

With  crossed  corn  the  situation  is  entirely  changed.  The  seed 
that  is  sold  is  used  to  produce  a  superior  crop  of  corn  but  this 
in  turn  can  not  be  used  for  further  planting  and  the  only  way 
the  same  result  can  be  secured  is  to  obtain  seed  from  the  original 
producer  each  year.  This  is  an  advantage  that  will  result  bene- 
ficially to  both  the  seedsman  and  the  one  who  plants  the  seeds. 
This  will  stimulate  the  production  of  better  kinds  of  corn  as 
nothing  else  has  ever  done.  Larger  crops  of  better  corn  will  be 
harvested  on  the  same  acreage  and  with  the  same  labor.  There- 
fore the  cost  of  producing  a  bushel  of  corn  will  be  reduced. 

At  this  Station  the  method  of  obtaining  good  inbred  strains  is 
as  follows.  A  variety  is  chosen  which  has  been  thoroughly  tested 
and  is  known  to  be  well  adapted  to  the  purposes  to  which  it  is  to  be 
put.  A  large  number  of  the  best  ears  of  this  variety  are  selected 
and  seed  from  each  ear  is  planted  in  a  separate  row  in  the  field. 
About  20  to  30  plants  are  grown  in  each  row.  When  the  plants 
are  ready  to  silk  out  five  of  the  best  plants  are  self-pollinated 
by  hand. 

This  is  a  simple  process  with  corn.  A  "three  pound"  paper  sack 
is  placed  over  the  ear  shoot  as  soon  as  it  appears  and  before  any 
silks  are  showing.  The  bag  is  slipped  over  the  ear  shoot  without 
being  opened  and  is  held  in  place  with  a  wire  paper  clip.  At  the 
same  time,  or  a  day  or  two  later,  an  "eight  pound"  bag  is  put 
over  the  tassel  and  securely  fastened  around  the  stalk  at  the  base 
of  the  tassel,  also  with  a  wire  clip. 

Two  or  three  days  later,  depending  upon  the  weather,  when 


CROSSED   CORN  i  7  I 

the  silks  are  out  about  three  inches  beyond  the  tip  of  the  ear,  the 
tassel  is  bent  over  and  shaken  into  the  tassel  bag  which  has  been 
unfastened.  This  collects  the  fine  yellow  powder,  the  pollen,  which 
is  dusted  over  the  silks.  The  small  bag  is  replaced  quickly  over 
the  ear  and  the  larger  tassel  bag  is  put  over  this,  thus  guarding 
against  breaks  in  the  bags  which  will  let  in  pollen  from  outside. 
The  bags  are  left  on  until  the  ears  are  gathered  in  order  to 
mark  them. 

Pollination  can  only  be  done  when  the  bags  are  dry.     Wet 


Fig.  17.- — Self-fertilizing  corn  by  hand  pollination. 


weather  or  heavy  dew  which  causes  the  pollen  to  clump  together 
renders  it  unfit  for  use.  Only  a  very  small  quantity  of  good 
pollen  is  needed  and  this  should  be  applied  as  soon  as  possible 
after  the  silks  appear. 

Care  is  taken  to  avoid  touching  the  silks  with  the  hands  and 
also  nearby  plants  are  pushed  away  so  that  their  pollen  will  not 
fall  on  the  silks.  Hand  pollination  in  this  way  insures  that  the 
ears  are  fertilized  with  pollen  from  the  same  plant.  This  is  the 
closest  kind  of  inbreeding  and  will  have  very  noticeable  effects  on 
the  resulting  progeny. 

An  inbred  strain  starting  from  an  ear,  borne  on  one  plant,  is 
called  a  self-fertilized  line.  From  the  five  hand  pollinated  ears 
made  the  first  vear  in  each  line,  three  of  the  most  desirable  are 


172 


CONNECTICUT    EXPERIMENT    STATION 


BULLETIN    273 


selected  for  planting-  the  next  year.  These  three  progenies  are 
grown  in  rows  and  two  plants  are  self-pollinated  by  hand  in  each 
row.  ■  . 


Fig.  18. — Two    self-fertilized   lines    from   the    same  variety   which 
differ  remarkably  in  height. 


CROSSED    CORN 


173 


Fig.  19. — Ability  to  stand  erect  has  a  basis  in  inheritance  as  these  two 
strains  were  derived  from  the  same  variety  and  grown  for  fifteen  years 
under  the  same  conditions. 


At  harvest  the  best  and  second  best  of  the  three  progenies  are 
noted  in  each  line.  Two  ears  from  the  best  and  one  from  the 
next  best  are  planted  the  following  year  and  this  system  is  fol- 


174 


CONNECTICUT   EXPERIMENT   STATION 


BULLETIN    2/3 


lowed  for  three  or  four  generations.  At  that  time  many  of  the 
lines  are  fairly  well  fixed  in  their  type  and  are  uniform. 

There  are  great  differences  between  the  several  lines.  Some  are 
tall,  others  short  and  all  degrees  in  between.  Some  have  many 
tillers,  others  have  few  or  none.  Differences  in  ability  to  stand 
erect,  in  amount  of  smut  damage,  mold  on  the  ears,  and  other 
characters  of  greater  or  less  importance  are  noted. 

Some  lines  are  so  unproductive  that  it  is  difficult  to  secure  any 
seed  from  them.  A  number  of  promising  strains  are  found  that 
make  a  fairly  good  ear  on  every  plant,  all  of  the  plants  stand  up 
during  the  season  and  have  qualities  that  make  them  appear  of 
value  although  few  of  them  are  more  than  half  as  productive  as 
the  variety  started  with.  Nearly  all  of  them  are  later  in  maturing 
than  the  variety  at  the  start  on  account  of  their  weakened  condi- 
tion. When  crossed  the  plants  grow  and  mature  much  faster  and 
the  value  of  the  inbreeding  process  is  at  once  apparent  in  the 
crossed  progenies. 

To  obtain  the  best  results  it  is  necessary  to  test  all  of  the  best 
appearing  inbred  strains  in  combinations  with  each  other.  This 
is  most  easily  done  by  hand-pollination,  putting  the  pollen  of  one 
strain  on  the  silks  of  the  other  and  keeping  a  record  of  the 
strains  combined. 


METHODS  OF  PRODUCING  CROSSED  SEED. 

When  a  good  combination  of  two  inbred  strains,  called  a  single 
cross,  is  once  found  it  is  a  comparatively  simple  matter  to  produce 
crossed  seed  in  quantity  by  planting  the  two  inbred  strains  in 
alternate  rows :   . 


A 


A 


B  etc. 


A  =  the  pollen  parent  rows ;  the  tassels  are  left  on  and  seed  from 
these  plants  is  inbred  and  can  be  used  for  planting  in  a 
crossing  plot  another  year. 

B  =  the  seed  parent  rows  with  all  the  tassels  pulled  out ;  seed 
from  these  plants  gives  crossed  corn. 

All  of  the  plants  of  one  kind  are  detasseled  before  any  pollen 
is  shed.  This  is  done  by  pulling  out  or  breaking  off  the  tassel 
as  soon  as  it  appears  above  the  leaves  at  the  top  of  the  stalks.  Pol- 
len is  scattered  by  the  wind  as  soon  as  the  anthers,  the  tiny  sacks 
suspended  on  short  threads  from  the  tassel  branches,  appear. 
These  are  put  out  first  at  the  tip  of  the  tassel  and  fresh  ones  come 
out  every  morning  for  several  days.     It  is  necessary  to  remove  all 


CROSSED    CORX 


175 


the  tassels  from  all  plants  of  one  kind  before  the  anthers  can  be 
seen.  If  pulled  too  soon  the  tassel  sometimes  breaks,  leaving  a 
portion  in  the  plant  which  will  later  grow  out  and  give  off  pollen. 
If  all  of  the  tassels  of  one  kind  of  plants  are  removed  at  the 
proper  time  all  of  the  seeds  produced  on  these  plants  must  be 
cross-pollinated  with  the  other  strain.  This  is  the  seed  to  be  used 
for  field  planting  and  will  give  vigorous  and  uniformly  produc- 
tive plants.  Seed  from  the  pollinator  rows  is  all  inter-pollinated 
and  can  be  used  for  stock  seed  for  planting  in  the  crossing  plot 


Fig.  20. — A  field  in  which  crossed  seed  corn  is  produced.  Two 
rows  are  detasseled  while  every  third  row,  planted  with  a  different  lot 
of  seed,  furnishes  the  pollen. 


next  year.  By  maintaining  two  crossing  plots  in  separate  fields, 
detasseling  one  type  in  one  field  and  the  other  type  in  the  second 
field,  it  is  possible  to  have  inbred  stock  seed  of  both  types  pro- 
duced each  year. 

Crossing  can  be  made  either  way  as  far  as  the  product  from  the 
crossed  plants  is  concerned.  Reciprocal  crosses  in  corn  give 
results  that  are  closely,  if  not  exactly  alike.  Usually,  however, 
it  is  desirable  for  one  reason  or  another  to  make  the  cross  one 
way.  Some  strains  make  better  seed  than  others  while  a  strain 
that  may  be  poorer  as  a  seed  parent  may  be  better  as  a  pollen 
parent.     If  this  is  the  case  a  small  plot  of  the  seed  parent  can  be 


i  70 


CONNECTICUT    EXPERIMENT    STATION 


BULLETIN    273 


grown  in  a  field  by  itself  to  produce  stock  seed  for  planting"  in 
the  crossing"  plot. 

It  is  very  important  to  maintain  the  stock  seed  of  the  two  in- 
bred types  free  from  any  outcrossing  with  any  other  corn. 
Pollen  is  blown  by  the  wind  for  long  distances.  Fields  that  are 
500  or  more  feet  apart  and  not  in  the  line  of  the  prevailing,  winds 
will  not  show  much  mixing  especially  if  they  are  separated  by  a 
barrier  of  trees  or  other  windbreaks. 


Fig.  21. — Two  inbred  strains  showing  uniformity  of  ear  type. 


Fortunately,  when  inbred  plants  are  crossed  with  any  unre- 
lated kind  of  corn  there  is  such  a  noticeable  increase  in  the  size 
of  the  crossed  plants  and  change  in  type  that  is  usually  possible 
to  detect  such  outcrosses  and  remove  them  before  they  produce 
pollen.  In  order  to  do  this  it  is  necessary  to  go  through  the  cross- 
ing fields  and  rogue  both  the  seed  parent  and  pollen  parent  very 
carefully  just  before  the  tassels  appear.  It  is  best  to  remove  or 
destroy  the  whole  plant  so  that  seed  from  them  will  not  get  mixed 
in  with  the  stock  strains. 


CROSSED    CORN 


177 


Generally  it  will  be  found  desirable  to  have  the  seed  parent 
early  in  order  to  have  the  crossed  seed  for  field  planting  well 
matured.  The  pollen  parent  can  be  later  since  pollen  usually 
comes  out  well  in  advance  of  the  silks.  A  small  difference  in 
this  order  will  bring  the  two  together  at  just  the  right  time. 

If  there  is  much  difference  in  time  of  silking  and  tasseling" 
betwetu  the  two  parental  stocks  it  is  necessary  to  plant  the  two 
at  different  times.  It  is  often  difficult  to  know  the  right  time  to 
plant  as  the  time  of  flowering  varies  with  the  season  and  changes 
unequally  with  different  strains. 


Fig.  22. — Crossing  the  two  inbreds  gives  size  and  retains  uniformity. 


Two  weeks  difference  in  planting  time  will  not  make  more  than 
four  or  five  days  difference  at  pollinating  time  as  the  late  planted 
corn  tends  to  catch  up  with  the  early.  However,  if  a  drv  spell 
or  other  unfavorable  growing  conditions  intervene  the  later  plant- 
ing may  not  come  on  as  fast  as  normally  whereas  the  earlier 
planted  corn  may  not  be  as  much  affected.  For  this  reason  it  is 
advisable  to  plant  the  pollen  parent  at  two  different  times,  from 
ten  days  to  two  weeks  apart.  When  the  seed  parent  and  pollen 
parent  flower  at  about  the  same  time  a  good  plan  is  to  plant  all  of 
the  seed  parent  and  half  of  the  pollen  parent  at  one  time,  leaving 
every  other  row  of  the  pollinator  to  be  planted  ten  davs  or  two 
weeks  later. 

With  vigorous  corn  it  is  not  necessary  to  have  the  pollen-produc- 
ing plants  in  every  other  row.  One  pollinating  row  to  two,  three 
or  even  four  detasseled  rows  is  sufficient  depending  on  the  amount 


i78 


CONNECTICUT    EXPERIMENT    STATION 


BULLETIN    273 


of  pollen  produced  and  the  duration  of  the  flowering  period. 
This  must  be  determined  by  trial  for  each  particular  combination 
and  the  field  in  which  it  is  grown. 


SINGLE  CROSSES. 

Hybrids  produced  by  combining1  two  fixed  inbred  strains  are 
called  single  crosses  and  have  the  greatest  uniformity  and  true- 
ness  to  type  in  the  first  generation  of  any  type  of  crossed  corn. 


Fig.  23. — Crossed  corn  showing  evenness  in  height  and  tassel  formation. 


Where  uniformity  in  size,  shape  and  other  ear  characters  and 
evenness  in  ripening  are  particularly  important,  as  in  sweet  corn 
for  market  gardening  and  canning,  it  will  probably  be  well  worth- 
while to  use  this  method  in  spite  of  certain  serious  handicaps. 

The  principal  difficulty  of  producing  single  crosses  is  the  low 
yields  and  poor  quality  of  the  seed  obtained  from  the  weakened 
inbred  plants.  No  inbred  strains  have  been  produced  that  will 
yield  much  more  than  half  as  much  as  the  original  variety  when 
dependent  upon  their  own  pollen  or  pollen  from  other  inbred 
strains.  They  also  make  a  much  smaller  amount  of  pollen,  and 
unless  the  two  strains  are  planted  at  just  the  right  time  so  that 


CROSSED    CORN 


J79 


pollen  will  be  given  out  as  soon  as  the  silks  appear,  and  continue 
until  all  the  silks  are  out,  the  amount  of  crossed  seed  produced 
will  be  very  low. 


Fig.  24. — All  of  the  ears  ripen  at  the  same  time. 


Inbred  strains  are  also  slower  in  ripening,  and  the  thorough 
curing,  so  necessary  to  insure  strong  germination,  is  difficult 
to  obtain. 


180  CONNECTICUT    EXPERIMENT    STATION  BULLETIN    273 

The  success  of  single  crossing"  will  depend  very  largely  on  the 
production  of  inbred  strains  which  are  sufficiently  vigorous  and 
productive  to.  make  a  fair  yield  of  seed.  Since  corn  is  being 
inbred  very  extensively  there  is  every  prospect  that  such  inbred 
strains  will  soon  be  forthcoming  and  that  this  method  can  be  used 
satisfactorily  with  sweet  corn  for  market  gardeners  and  canners. 


DOUBLE  CROSSES. 

A  further  development  of  the  method  of  crossing  has  been 
made  which  overcomes  the  handicap  of  low  production  and  poor 
quality  of  seed  of  the  first  method.  This  is  to  cross  two  first 
generation  hybrids.  In  this  way  four  different  inbred  strains 
are  combined  by  three  crossings  as  follows: 

Inbred  Strains   A 

Single  Crosses    A 


Double   Cross    

The  two  crosses  of  inbred  strains  are  made  as  described  above. 
The  two  different  lots  of  crossed  seeds  are  planted  in  alternating" 
rows  in  the  same  way  and  all  the  plants  of  one  lot  are  detasseled 
in  the  same  way  as  before.  The  seed  produced  on  the  detasseled 
plants  is  used  for  field  planting.  The  seed  from  the  plants  that 
produced  the  pollen  is  of  no  further  value  either  for  field  planting 
or  for  stock  seed  and  must  be  discarded. 

The  two  single  crosses  being  vigorous  and  productive,  a  good 
yield  of  high  quality  seed  is  obtained.  The  crosses  produced  in 
this  way  by  one  hybrid  type  pollinated  by  another  are  no  less 
productive  than  either  parent  and  production  may  even  be  appreci- 
ably increased. 

It  is  important  to  test  the  combinations  first  but  when  a  high 
yielding  and  desirable  double  cross  is  once  produced  it  can  always 
be  reproduced  by  combining  the  same  strains  in  the  same  way. 

It  is  essential  that  the  four  inbred  strains  be  of  such  constitu- 
tion that  they  will  give  good  results  in  all  combinations  when 
crossed  singly,  particularly  the  crosses  AC,  AD,  BC  and  BD. 
The  combinations  AB  and  CD  should  also  grow  well  to  give  a 
good  yield  of  seed.  The  four  strains  may  all  come  from  the  same 
variety  or  from  different  varieties.  In  the  latter  case  the  two 
strains  which  form  the  seed  parent  should  come  from  one  variety 
and  the  two  to  form  the  pollen  parent  from  the  other. 

Double  crosses  are  not  as  uniform  as  single  crosses  either  in 
height  of  plant,  size  and  shape  of  ear,  or  in  time  of  maturity- 


CROSSED    CORN 


Fig.  25. — Illustrating  by  actual  field  results  the  bring- 
ing together  of  four  inbred  strains  by  three  crossings 
to  produce  double  crossed  corn. 


1 82  CONNECTICUT   EXPERIMENT    STATION  BULLETIN    273 

This  is  due  to  the  fact  that  the  first  generation  hybrids  used  for 
the  seed  and  pollen  parents  are  all  producing  ovules  and  pollen 
grains  of  unlike  germinal  constitution.  However,  all  of  the 
double  crossed  plants  result  from  hybrid  combinations.  There  is  no 
opportunity  for  weaknesses  to  appear  due  to  inbreeding.  Hybrid 
vigor  is  therefore  kept  at  the  maximum  and  may  even  be  increased. 
For  that  reason  every  plant  is  strong  and  sturdy  and  each  one 
produces  a  good  ear  if  given  an  equal  chance  to  grow. 

In  field  corn  where  uniformity  is  not  so  important  the  greater 
variability  of  double  crosses  may  be  an  advantage  in  giving  the 
plants  a  greater  adaptiveness  to  different  seasons  and  soils.  All 
of  the  plants  will  not  be  at  the  same  critical  stage  of  development 
at  some  unfavorable  period  and  may  escape  injury  that  would 
seriously  damage  a  more  uniform  lot  of  plants. 

The  productiveness  of  a  double  cross  compared  to  the  single 
crosses  and  the  original  varieties  is  shown  in  the  following  com- 
bination of  inbred  strains  self-fertilized  four  years,  two  strains 
from  Century  Dent  and  two  from  Learning.  Both  varieties  have 
been  grown  for  many  years  in  Connecticut,  are  well  adapted  to 
local  conditions  and  are  among  the  highest  yielding  of  all  the 
varieties  tested  at  Mt.  Carmel  and  at  Storrs. 

Variety  or  Cross  Yield  in  Bu.  per  Acre 

Century  Dent,  no   47.5 

Learning,    112    44.4 

Inbred  Century  Strain,  110-2  15.3 

Inbred  Century  Strain,   110-4   16.8 

Inbred  Learning  Strain,  112-1   42.7 

Inbred  Learning  Strain,   112-4   11.1 

Single  Cross,   110-2x110-4   51.2 

Single  Cross,   112-1x112-4   45-6 

Double  Cross    (no-2x  110-4)  x  (112-1  x  112-4)  .  69.8 

The  figures  represent  averages  of  from  two  to  six  plots  of  each 
lot.  The  yields  have  been  corrected  for  soil  differences  according 
to  results  from  the  adjoining  check  plots  and  all  are  based  on  a 
uniform  moisture  content  of  12  per  cent.  The  double  cross  gave 
over  50  per  cent  more  grain  than  the  average  of  the  two 
parental  varieties. 

The  yield  of  one  of  the  inbred  strains  is  unusually  high,  nearly 
equalling  the  variety  from  which  it  was  derived.  The  quality  of  the 
inbred  corn  was  poorer  than  the  variety  and  this  yield  was 
obtained  in  a  field  where  there  was  an  abundance  of  pollen.  When 
planted  in  a  separate  field  and  dependent  on  its  own  pollen  or 
pollen  from  another  inbred  strain  it  would  probably  not  yield 
so  high. 

A  combination  of  two  inbred  strains  of  Burr's  White  Dent  and 
two  of  Learning,  both  varieties  originally  from  Illinois,  has  been 
found  to  give  a  large  and  vigorous  stalk  growth  and  generally 


CROSSED    CORN 


l83 


a  higher  yield  of  grain  than  any  variety  of  corn  grown  in  southern 
Connecticut.  This  particular  combination  is  called  Double  Crossed 
Burr-Learning  and  seed  has  been  grown  commercially  since  192 1. 
From  1918  to  1922  it  was  tested  at  Mt.  Carmel  in  comparison 
with  all  of  the  varieties  commonly  grown  in  Connecticut  and  the 
yields  are  given  in  the  first  part  of  this  bulletin. 

This  combination  yielded  more  than  all  varieties  in  three  out 
of  the  five  years  tested,  while  no  one  variety  yielded  more  than 


Fig.  26. — Double  Crossed  Burr-Learning'. 


the  others  in  more  than  one  year.  The  greater  return  from  Burr- 
Learning  is  not  only  in  the  larger  yield,  but  also  in  the  freedom 
from  mold,  fewer  nubbins  and  less  soft  corn.  In  addition  the 
plants  have  a  noticeable  ability  to  stand  erect  when  other  varieties 
are  blown  down,  and  show  a  marked  tendency  to  hold  their  foliage 
green  until  the  seeds  are  ripe. 

Although  this  new  kind  of  corn  will  not  out-yield  all  varieties, 
everywhere,  in  each  season,  it  has  been  tested  sufficiently  under 
farm  conditions  to  show  that  it  can  be  planted  profitably  in 
many  places. 


I.84  CONNECTICUT    EXPERIMENT    STATION  BULLETIN    273 

Double  crosses,  like  single  crosses,  will  not  maintain  their  high 
yields  more  than  one  year  after  the  cross.  From  a  field  of 
Double  Crossed  Burr-Learning  that  yielded  well  over  one  hundred 
bushels  of  shelled  grain  per  acre,  about  one  bushel  of  the  largest 
and  finest  ears  were  selected.  These  were  shelled  together  and 
this  second  generation  seed  was  planted  the  following  year  in 
comparison  with  first  generation  seed.  Two  plots  averaged  73.5 
bushels  in  comparison  with  95.1  bushels  for  the  freshly  crossed 
seed.  This  is  a  loss  in  grain  of  23  per  cent.  The  stalks  grew 
vigorously  and  from  the  appearance  in  the  field  it  seemed  to  be 
as  productive  as  the  first  cross  but  at  harvest  time  it  was  seen 
that  many  plants  failed  to  make  a  good  ear. 


MULTIPLE  CROSSES. 

The  principal  objection  to  the  method  of  double  crossing  is  the 
necessity  of  maintaining  four  inbred  strains  of  corn  free  from 
outcrossing  with  each  other  or  other  types  of  corn  and  making 
three  separate  crosses. 

Theoretically,  the  same  combinations  of  factors  and  in  the  same 
proportions  can  be  secured  by  crossing  the  second  generations 
from  the  two  single  crosses  as  by  crossing  the  two  first  genera- 
tion hybrids.  A  two  years  test  shows  that  in  the  case  of  the 
Burr-Learning  combination  the  second  generation  of  the  Burr 
White  single  cross  by  the  second  generation  of  the  Learning 
single  cross  gives  the  same  yield  and  quality  of  corn  as  the  com- 
bination of  the  first  generations  of  those  two  crosses.  The  yield 
and  quality  of  the  seed  itself  produced  by  second  generation  plants 
is  not  so  good  but  the  crop  grown  from  that  seed  is  in  every  way 
equal  to  the  combination  of  the  two  first  generation  hybrids. 

These  results  led  to  "multiple  crosses,"  a  further  step  in  the 
evolution  of  crossed  corn.  A  number  of  the  best  inbred  strains 
of  a  variety  are  permanently  combined  into  a  fairly  uniform  type 
that  can  be  propagated  from  year  to  year  by  natural  inter-crossing, 
as  are  ordinary  varieties.  In  other  words,  a  "re-created"  variety 
is  produced  in  which  all  the  best  of  the  old  variety  has  been  com- 
bined and  all  the  inherited  abnormalities  and  weaknesses  have 
been  eliminated. 

This  recreated  variety  is  now  crossed  with  a  similar  combina- 
tion of  the  best  inbred  strains  from  some  other  sort  or  perhaps  a 
group  of  inbred  strains  of  different  type  from  the  same  variety. 

Such  a  multiple  cross  would  have  the  advantage  of  producing 
good  yields  of  well  developed  seed  and  crossing  each  year  would 
give  maximum  vigor  and  productiveness.  This  method  has  not 
yet  been  thoroughly  tested  but  preliminary  tests  indicate  that  it 
will  be  feasible.     The  uniformity  of  the  crossed  plants  produced 


CROSSED   CORN 


iSc 


by  this  method  may  not  be  as  great  as  in  a  double  cross,  but  if 
the  right  combination  of  strains  is  made,  yield  should  be  maintained 
at  a  high  level  indefinitely. 


MODIFIED  SINGLE  CROSSES. 

Greater  uniformity,  where  this  is  desirable,  can  be  obtained  by 
combining  a  number  of  strains  from  one  line  descending  from  a 


Fig.  27. — The  uniform  size  and  shape  of  ear  and  even  ripening  are 
important  factors  in  sweet  corn  for  market  gardening  and  canning. 


single  plant  but  separated  in  the  first  or  second  generation  and 
self-fertilized  four  or  five  years  to  rid  them  of  recessive  weaknesses 
and  undesirable  characters.  Combining  several  of  these  sub- 
strains gives  vigor  and  productiveness  closely  approaching  the 
original  variety  and  such  a  combination  could  be  propagated  from 


lS6  CONNECTICUT    EXPERIMENT    STATION  BULLETIN    273 

year  to  year  by  natural  inter-pollination,  at  the  same  time  main- 
taining" a  fair  degree  of  fixity  of  type. 

When  crossed  with  a  similar  combination  of  sub-strains  descend- 
ing from  a  different  plant  of  the  same  or  a  different  variety 
yield  and  vigor  would  be  as  great  as  in  any  system  of  crossing 
and  the  uniformity  of  the  hybrid  in  certain  combinations  would  be 
nearly  as  pronounced  as  in  straight  single  crosses  of  two  fixed 
inbred  strains. 

Crossed  seed  for  field  planting  would  be  made  each  year.  The 
yield  and  quality  of  the  seed  would  be  better  than  that  produced 
by  single  inbred  strains  and  nearly  equal  in  these  respects  to  the 
method  of  double  or  multiple  crossing. 


UNIFORMITY  AND  YIELD. 

In  all  of  these  methods  of  crossing  one  must  compromise 
between  the  uniformity  of  the  crossed  corn  on  the  one  hand  and 
the  vigor  and  productiveness  of  the  stock  strains  used  in  making 
the  cross  on  the  other. 

Where  uniformity  is  of  great  importance  it  will  be  best  to  use 
the  method  of  crossing  two  fixed  and  uniform  inbred  strains. 
Where  trueness  to  type  is  not  so  important,  as  in  field  corn  for 
grain  or  silage,  maximum  yields  can  be  obtained,  at  a  lower  cost, 
by  double  crosses  or  multiple  crosses. 

In  all  systems  of  crossing  inbred  strains  the  variability  of  the 
crossed  corn  is  no  greater  than  is  now  present  in  all  varieties  of 
corn  and  is  frequently  less  because  every  plant  is  vigorous  and 
productive  and  much  poor  corn  that  is  usually  harvested  from 
every  field  is  largely  eliminated. 


NECESSITY  OF  USING  CROSSED  SEED. 

All  of  these  methods  of  crossing  may  seem  complicated  to  those 
who  are  not  familiar  with  the  development  of  corn  breeding-  prac- 
tices. It  is  only  necessary  to  remember,  however,  that  two  sepa- 
rate strains  of  corn  must  be  maintained  free  from  mixing  with 
each  other  or  any  other  kind  of  com  and  that  these  two  types 
must  be  planted  in  alternating  rows  and  all  the  plants  of  one  of 
them  detasseled  before  pollen  is  shed.  The  seed  produced 
on  these  castrated  plants  is  used  for  planting  to  produce 
crossed  corn. 

The  experience  of  twenty  years  indicates  clearly  that  the  largest 
yields  together  with  the  greatest  uniformity  and  fixity  of  type 
adapted  to  particular  requirements  can  only  be  obtained  by  some 
system  of  crossing.     Furthermore  the  evidence  is  conclusive  that 


CROSSED   CORN  1 87 

these  crosses  will  not  maintain  their  high  yields  and  other  desirable 
qualities  in  later  generations,  so  that  to  secure  the  benefits  of 
hybrid  vigor  it  is  necessary  to  plant  crossed  seed  every  year. 


COST  OF  SEED  CORN. 

It  requires  about  ten  bushels  of  potatoes  to  plant  an  acre.,  about 
two  bushels  of  oats  and  a  bushel  and  a  half  of  wheat  for  a 
similar  area. 

Depending  upon  the  size  of  the  kernels  and  the  rate  of  planting 
a  bushel  of  corn  will  plant  from  four  to  seven  acres.  For  dent 
corn  five  quarts  of  seed  is  usually  ample  for  each  acre. 

While  the  value  of  seed  corn  is  somewhat  more  in  proportion 
to  the  market  value  of  the  grain  for  corn  than  other  commonly 
cultivated  crops,  the  cost  per  acre  of  the  seed  is  the  lowest  of  the 
list,  and  compared  to  the  other  expenses  of  growing  a  crop  of 
corn,  the  preparation  of  the  soil,  application  of  fertilizers,  fre- 
quent cultivation,  husking  out  or  cutting  up  for  silage,  the  cost  of 
the  seed  becomes  almost  a  negligible  item. 

For  this  reason  the  outlay  for  seed  may  be  considerably 
increased,  even  doubled  or  tripled,  and  still  be  repaid  many  times 
over  if  the  high  priced  seed  gives  an  appreciable  increase  in  yield 
or  improvement  in  quality. 

Crossed  corn  can  do  this.  It  has  been  tested  long  enough  to 
show  that,  when  the  right  combination  is  obtained,  one  which  is 
adapted  to  the  locality  in  which  it  is  to  be  grown,  it  will  easily 
pay  for  the  increased  cost  of  the  seed,  and  leave  a  margin  of 
profit  as  well. 


•     if.       05 


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